The present invention relates generally to apparatuses for inspecting magnetic disks. More particularly, the invention concerns an inspection method and apparatus suitable for detecting magnetic-disk surface defects in magnetic recording characteristics as well as in appearance.
Magnetic disks (storage media) are becoming enhanced in recording density each year, and this tendency is making it necessary to dimensionally manage smaller disk-surface defects during manufacturing processes. At the same time, the increase in recording density is calling for the suppression of an increase in the time required for the read/write tests conducted to inspect recording states by writing data onto magnetic disks and reading out the data.
A technique for responding to such needs is disclosed in JP-A-11-86282 (Patent Document 1). JP-A-11-86282 describes a read/write test method including: first, inspecting magnetic disks optically with an optical inspection apparatus and detecting defects thereof; next dividing the inspected magnetic disks into groups based on detected defect data; and activating a certification test apparatus to write data, with a magnetic head, only onto any magnetic disks that have been determined to be of the group requiring electrical characteristics inspection, then read out the written data from each magnetic disk, and inspect a recording state of the magnetic disk.
Another related technique is disclosed in U.S. Pat. No. 6,057,962 (Patent Document 2). U.S. Pat. No. 6,057,962 describes a read/write test method that including: first, inspecting the surfaces of magnetic disks optically with an optical inspection apparatus and removing any magnetic disks found to have particles sticking to the disk surface; next after sampling some of the non-removed magnetic disks, activating an apparatus to write data onto each sampled magnetic disk using a magnetic head, then read out the written data, and inspect a recording state of the magnetic disk.
As the recording densities of magnetic disks (storage media) are enhanced, the flying heights of magnetic heads during the rotation of the magnetic disks are coming to decrease, and even magnetic disks with smaller particles or projections or depressions on the surface thereof may be determined to be defective, during read/write tests. This indicates that even the magnetic disks whose surfaces have been optically inspected with an optical inspection apparatus and determined to be non-defective may have, on the surface, such small particles or projections or depressions that cause the disk to be recognized as a defective one during read/write tests.
Accordingly, as described in Patent Document 1, even if disk surface defect optical inspections with an optical inspection apparatus indicate the presence of no defective magnetic disks, some of these disks may require electrical characteristics inspection, or read/write tests, according to a particular surface state.
In the magnetic disk inspection methods described in Patent Documents 1 and 2, data on the defects that were detected during optical inspection of magnetic disk surfaces with an optical inspection apparatus has not been utilized during read/write tests. Since read/write tests require a greater deal of inspection time than that for optical inspection, it is absolutely necessary that several sampled areas on the magnetic disk be inspected on a mass-production line basis. In the above conventional methods, however, since optical inspection result information has not been used during sampling-position selection for the read/write tests, inspection has only been possible by sampling predetermined positions on the magnetic disk independently of the defect positions.